Clarification on 73+ brakes

You may or may not need a proportioning valve it depends on the overall setup and what tires you run, wheel cylinder/ brake size, etc, etc.

You can use the original block which should also be the warning light switch.

I'm using Versailles rear disc with mine, and even used my same master.........just poked nails through the residual valve rubbers at the master fittings

I see nothing wrong with the description of your caliper mount, you will need longer hoses. Someone posted the other day?? 69 camaro?? hoses, otherwise use Volare hoses